Rust for linux CI breaks with rust 1.86

[emilio]

See https://github.com/rust-lang/rust-bindgen/actions/runs/14266991678/job/39991122643 for some of the failures.

#3186 disabled this temporarily, #3187 enabled it by downgrading to 1.85.1.

@ojeda any chance you can look whenever you have some time? Thanks.

[ojeda]

Sorry for the trouble, and thanks for taking a look!

This should be fixed if we upgrade to v6.14-rc2 or later, since the fix for that issue landed there (but it wasn't in -rc1).

I would say, let's go directly to v6.14 anyway: #3189